Decorative sheets have been developed and advanced in the process of growth of the residential building industry. In particular, apartments and condominiums, which are collective residences, and prefabricated houses, which are individual residences, have played the leading role.
Housings have been conventionally built by using materials such as woods and stones indigenous to each region, and in a style rooted to a specific culture. However, as industrialization has spread with development of residential industry, natural materials have been replaced with artificial materials. In addition, frequent use of high grade wood materials and stone materials in recent years, which may lead to a risk of deforestation and environmental problem, also contributes to the expansion of demand for decorative sheets.
In recent years, improvements in scratch resistance of sheet surface have been required in the performance of decorative sheets, and a large number of various improvements have been reported. One of such improvements is to provide a protective layer on a front layer of a decorative sheet. In particular, use of heat-curable resin, UV-curable resin, or electronic beam-curable resin is commonly known (for example, see PTL 1).
Thus, in processing of decorative sheets into decorative materials such as decorative boards, there is often a demand to provide decorative sheets without having quality defects such as wrinkle and flare.